Method for manufacturing mesoporous alumina molecular sieve and alumina nanotube and use of the alumina nanotube for storage of H2

ABSTRACT

A mesoporous alumina molecular sieve and a method of manufacturing a mesoporous alumina mesoporous alumina molecular sieve of the invention is produced without using traditionally used additives. Also, because the size and distribution of the pores can be controlled, the molecular sieve can be produced simply and economically, producing molecular sieve with high surface area and thermal stability. Further, a method of manufacturing an alumina nanotube by using a surfactant and a use of the alumina nanotube as a hydrogen storage material are provided.

CROSS REFERENCE TO RELATED APPLICATION

This application is a 35 U.S.C. § 371 National Phase Entry Applicationfrom PCT/KR02/01951, filed Oct. 18, 2002, and designating the U.S.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of manufacturing a mesoporousalumina molecular sieve and an alumina nanotube by using a surfactantand a use of the alumina nanotube as a hydrogen storage material.

2. Description of the Related Art

Generally, alumina is considered an important catalyst and support inindustrial processes. A reaction of mesoporous alumina with uniformporosity, high surface area, chemical stability and thermal stability isbecoming more valuable than existing alumina with non-uniform poredistribution.

Various surfactants, such as cationic, anionic, neutral and nonionicsurfactants have been used in producing alumina with mesopores.Specifically, there have been reports in producing alumina withmesopores and high surface area, by using a nonionic surfactant, asodium dodecyl sulfate and a long chain carboxylic acid.

However, due to an extremely rapid hydrolysis of alumina in an aqueoussolution, it is difficult to synthesize mesoporous alumina molecularsieve using a cationic surfactant. Even in the presence of a surfactant,a hydrated hydroxide in a lamellar form can be produced. Therefore,additives such as triethanoleamine, a hydrolysis inhibitor, are added toprevent rapid hydrolysis in synthesizing mesoporous alumina molecularsieve. Currently, a method of producing mesoporous alumina molecularsieve with high surface area, good thermal stability and simpleproduction method is in demand.

Hitherto, there have been reports on methods of producing mesoporousalumina materials with pore structures of a wormhole or sponge-likemotifs by utilizing a supramolecular assembly phenomenon of asurfactant, but there are no reports on producing alumina nanotube byusing surfactants.

There have been reports on the reaction of alumina fiber in anano-structure, by sol-gel process, in which temperature is continuouslyraised until a predetermined cut-off temperature. There have also beenreports on the reaction of alumina nanotube by an electrochemicalanodizing method. However, these processes cannot produce a large amountof alumina nanotube.

There has been no report regarding the usage of an alumina nanotube as ahydrogen storage material.

Hydrogen is considered an infinite energy source since hydrogen can beobtained from the earth's water source and it can be recycled back intowater form after combustion. Hydrogen is a clean energy source since itproduces only water, and not environmental pollutants during combustion.Hydrogen energy can be used in almost all industries, includingtransportation and electricity generating systems. However, a problem inusing the hydrogen energy has been raised due to lack of developments onsimple and economical hydrogen storage system.

Hydrogen can be physically stored in a high-pressure chamber bycompressing the hydrogen beyond 100 atm. But loading the chamber on atransportational vehicle is extremely dangerous. Also, another physicalstorage method involves storing the hydrogen at an extremely lowtemperature, below its boiling point (20.3K). However, although thismethod allows storing large amount of hydrogen by reducing the storagevolume, the cost of equipments used in maintaining the low temperatureis too high.

Hydrogen can be chemically stored by using a hydrogen storage alloy.Although such method efficiently stores hydrogen, with repeated cycle ofstorage and release of hydrogen, impurities may enter and causedeformation of the hydrogen storage alloy, which leads to adeterioration of the hydrogen storage capacity. Also, because a metallicalloy is used as the storage medium, the weight per unit volumeincreases, thus, it is difficult to load the storage alloy onto atransportation instrument.

Another hydrogen storage method is achieved by forcing adsorption ofhydrogen gas on to a solid material. Among such methods, hydrogenstorage by carbon nanotube or nano-structured carbon materials showshydrogen storage efficiency exceeding 10 wt. %. However, these resultsare difficult to reproduce and many researches are continuing toovercome problems caused by such method.

There are ongoing active researches to develop a hydrogen storage methodthat reaches at least 6.5 percent by weight of storage efficiency, whichis the target hydrogen storage required by the US Department of Energy(DOE), while providing stability and economical efficiency.

SUMMARY OF THE INVENTION

The present invention provides a mesoporous alumina molecular sieve witha high surface area and an outstanding thermal stability, produced in amoderate reaction condition with no other additives than a surfactant.The invention further provides a method of producing the same.

According to an aspect of the present invention, there is provided amethod of producing an alumina nanotube that can be mass produced in amoderate reaction condition by using a surfactant.

According to another aspect of the present invention, there is provideda hydrogen storage method that is more efficient, reliable,reproducible, and economical than currently available hydrogen storagemethods, by using the alumina nanotube of the foregoing.

An embodiment of the present invention provides a method of producing amesoporous alumina molecular sieve achieved by mixing a surfactant andan alumina precursor with an organic solvent to produce a mixture,adding water to the mixture, hydrothermal synthesizing the mixture withadded water, and then drying and calcinating the mixture to removeresidual surfactants.

The alumina precursor to water mole ratio should be 1:0.1 to 10 for theabove embodiment.

The alumina precursor to water mole ratio should be 1:1 to 3 for theabove embodiment

The surfactant to water mole ratio should be 1:0.1 to 10 for the aboveembodiment.

The surfactant is a cationic surfactant for the above embodiment.

The cationic surfactant is of chemical formula 1 below;

wherein R₁ to R₃ represent substituted or unsubstituted alkyl group with1 to 4 carbon atoms, R₄ represents substituted or unsubstituted alkylgroup with 8 to 22 carbon atoms, and x represents a halogen atom,acetate, phosphate, nitrate, or methylsulfate.

The alumina precursor should be an aluminum alkoxide, for example,aluminum-tri-butoxide or an aluminum isopropoxide.

According to an embodiment of the present invention, the organic solventshould be a solvent belonging in an alcoholic group of organic solventssuch as 1-butanol, 2-butanol, 1-propanol or 2-propanol.

According to an embodiment of the present invention, the hydrothermalreaction is carried out at 0 to 200° C. for 10 to 100 hours.

Another embodiment of the present invention provides a mesoporousalumina molecular sieve produced by using any the methods described inthe foregoing.

Another embodiment of the present invention provides a method ofproducing alumina nanotube achieved by mixing a surfactant and analumina precursor with an organic solvent to produce a mixture, addingwater to the mixture, hydrothermal synthesizing the mixture with addedwater, and then drying and calcinating the mixture to remove residualsurfactants.

According to an embodiment of the present invention, lithium precursormay be added during the mixing the surfactant and the alumina precursorstep or after the drying and calcinating process. The lithium precursorand water is added after the calcinating process to induce ion exchangeand further dried and calcinated to produce an alumina nanotube withlithium seed and again adding the lithium precursor by impregnationmethod followed by calcinating process.

According to another embodiment of the present invention, the lithiumprecursor may be lithium hydroxide, halide, nitrate, carbonate orsulfate.

According to another embodiment of the present invention, the aluminaprecursor to the lithium precursor mole fraction is 1:0.1 to 10. Evenmore preferably 1:1 to 3 mole fraction.

According to another embodiment of the present invention, the aluminaprecursor to surfactant to water mole ratio is 1:0.1 to 10:0.1 to 10.

According to another embodiment of the present invention, the surfactantshould be a cationic surfactant of chemical formula 1 below, an anionicsurfactant of chemical formula 2 below, a nonionic surfactant ofchemical formula 3 below, or a neutral surfactant of chemical formula 4below;

wherein R₁ to R₃ represent substituted or unsubstituted alkyl group with1 to 4 carbon atoms, R₄ represents substituted or unsubstituted alkylgroup with 8 to 22 carbon atoms, and x represents a halogen atom,acetate, phosphate, nitrate, or methylsulfate.R₅—COOH  [Chemical Formula 2]wherein R₅ represents substituted or unsubstituted alkyl group with 1 to22 carbon atoms.CH₃(CH₂)₃₀(CH₂CH₂O)_(n)—OH  [Chemical Formula 3]wherein n represents an integer of 1 to 30.R₆—NH₂  [Chemical Formula 4]wherein R₆ represents substituted or unsubstituted alkyl group with 8 to22 carbon atoms.

According to another embodiment, the aluminum precursor should be analuminum alkoxide, for example, aluminum-tri-butoxide or an aluminumisopropoxide.

According to another embodiment, the hydrothermal reaction should becarried out at 0 to 200° C. for 10 to 100 hours.

According to an embodiment of the present invention, there is providedan alumina nanotube produced by the above methods.

According to another embodiment of the present invention, there isprovided a hydrogen storage material produced by inducing adsorption ofhydrogen to the aluminum nanotube.

The hydrogen storage material, wherein the adsorption of hydrogen iscarried out while maintaining temperature of a container holding thenanotube at 298K to 673K and maintaining the pressure of hydrogen gas at1 to 10 atmospheric pressure. The hydrogen storage material of abovewherein the container holding the nanotube is vacuum treated at 373K to773K prior to inducing hydrogen adsorption.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent by describing in detail exemplary embodimentsthereof with reference to the attached drawings in which:

FIG. 1 is a TEM photograph and SADP pattern of an alumina nanotubeproduced according to Example 2-6 of the invention;

FIG. 2 a are HR-TEM photographs of an alumina nanotube with lithium,produced according to Example 2-10 of the invention

FIG. 2 b are TEM photographs of an alumina nanotube with lithium,produced according to Example 2-10 of the invention;

FIG. 3 is a TEM photograph of an alumina nanotube with lithium, producedaccording to Example 2-14 of the invention;

FIG. 4 represents a diagram for a constant volume system to test thehydrogen storage capacity of the alumina nanotube;

FIG. 5 is a graph depicting the result of hydrogen storage capacityexperiments of the alumina nanotube with lithium produced in Example 10,under constant pressure (2.7 atmospheric pressure) but at differenttemperatures.

FIG. 6 depicts the results of ¹H NMR showing the adsorption anddesorption of hydrogen at 2.7 atmospheric pressure and room temperatureof the alumina nanotube with lithium produced in Example 10;

FIG. 7 is a TEM photograph of mesoporous alumina molecular sieveproduced according to Example 1-5 of the invention; and

FIG. 8 is a graph depicting the X-ray diffraction pattern of themesoporous alumina molecular sieve produced according to Example 1-4 ofthe invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides a method of producing a mesoporous aluminamolecular sieve by using a surfactant and an alumina precursor in amoderate reaction condition.

In the method of producing mesoporous alumina molecular sieve accordingto the present invention, the hydrolysis rate of an alumina precursorcan be controlled simply by using a surfactant and water mixed in astoichiometric ratio in an alcohol-based organic solvent, even withoutcommonly used additives such as triethanolamine. As a result, theproduction of hydrate hydroxides, caused by rapid hydrolysis, can beminimized. Also, by manipulating the reaction condition and the lengthof the surfactant's tail, the size and distribution of the mesopores ofthe alumina molecular sieve can be controlled.

The mesoporous alumina molecular sieve of the invention is produced bymixing a surfactant and an alumina precursor in an organic solvent toform a mixture. Afterwards, water is slowly added to the mixture,followed by hydrothermal reaction, drying and calcination processes toremove residual surfactants.

As a surfactant, any of the surfactants commonly used in the field maybe used. However, preferably, a cationic surfactant is used and morepreferably, a cationic surfactant as represented by the followingChemical Formula 1 is used.

wherein R₁ to R₃ represent substituted or unsubstituted alkyl group with1 to 4 carbon atoms, R₄ represents substituted or unsubstituted alkylgroup with 8 to 22 carbon atoms, and X represents a halogen atom,acetate, phosphate, nitrate, or methylsulfate.

Examples of the cationic surfactant of the Chemical Formula 1 includeCH₃(CH₂)_(n-1)N(CH₃)₃Br (wherein n is 12, 14, 16 or 18) andCH₃(CH₂)_(n-1)N(CH₃)₃Cl (wherein n is 12, 14, 16 or 18). Since the sizeof a mesopore depends on the length of the cationic surfactant's tail,an appropriate cationic surfactant with desired tail length may bechosen in producing mesopores with a predetermined size.

Preferably, the amount of surfactant is 0.1 to 10 mole per 1 mole ofalumina precursor. At an amount of less than 0.1 mole ratio, thesurfactant may not effectively form micelle structures and at an amountgreater than 10 mole ratio, it is not cost effective to use such surplusamount of surfactants.

As an alumina precursor, any commonly used material in the field may beused. However, preferably, an aluminium alkoxide, such as aluminiumtri-sec-butoxide and aluminium isopropoxide is used.

In conventional methods, the alumina precursor such as aluminum alkoxideundergoes rapid hydrolysis, forming hydrated hydroxide so that additivesare used to restrain hydrolysis. However, in the present invention, thehydrolysis rate can be controlled simply by adding water, without addingadditives.

Preferably, the amount of water for hydrolysis is in a stoichiometricratio to the alumina precursor. Preferably, water is added slowly into amixture of an alumina precursor and a surfactant in an organic solvent.Also preferably, the stoichiometric ratio of water to aumina precursoris 0.1 to 10 mole of water per 1 mole of alumina precursor and morepreferably 1 to 3 mole of water per 1 mole of alumina precursor. At anamount less than 0.1 mole ratio, an effective hydrolysis of aluminiumprecursor is unlikely to take place, and at an amount greater than 10mole ratio, the hydrolysis rate would increases due to large amount ofwater, making the formation of uniform mesopores difficult.

Preferably, the organic solvent for the invention is an alcohol-basedorganic solvent, such as 1-butanol, 2-butanol, 1-propanol and2-propanol.

In the process of the invention for preparing a molecular sieve, themixture of a surfactant and an aluminium precursor in an organic solventis added with water and then is subjected to hydrothermal reaction. Thepurpose of the hydrothermal reaction is to form an alumina mesoporeprecursor by a dehydration reaction of the mixture. Preferably,temperature during the reaction is 0 to 200° C. and the reaction lasts10 to 100 hours.

After the hydrothermal reaction, drying and calcination processes arecarried out to produce a mesoporous alumina molecular sieve. Preferably,the drying process is carried out at a room temperature or at asufficiently high temperature to effectively remove un-reacted materialsand solvents. The temperature may vary according to the amount of addedwater and solvents. The purpose of the calcination process is to removeresidual surfactants. Preferably, the process is carried out at an inertatmosphere or at an air atmosphere for 1 to 10 hours at 200 to 800° C.

Unlike conventional methods, the present method allows for theproduction of mesoporous alumina molecular sieve with controlled poresize and pore distribution. Also, because the hydrolysis rate is slow,formation of hydrated hydroxide is suppressed, resulting in homogenizedformation of the mesoporous alumina molecular sieve. Further, it iseconomical since additives are not used.

The invention further includes a method of producing an alumina nanotubeby using a surfactant, an alumina precursor and water in a moderatecondition, without solvents or additives.

In the present invention, an alumina nanotube is produced by asurfactant and water mixed in a stoichiometic ratio without usingsolvents or additives. The synthetic reaction is performed at atemperature of approximately 150° C. or lower to encourage simple dryingof the mixture and separation of the product.

The invention further includes an alumina nanotube with lithium. Thelithium can be added simultaneously or following the alumina nanotubereaction. When adding lithium after nanotube reaction, ion-exchangemethod or impregnation method is used to incorporate lithium into thealumina nanotube.

The alumina nanotube of the invention weighs less and is better capableof safely storing large amount of hydrogen compared to other hydrogenstorage materials that use hydrogen storage alloy or carbon nanotubes.Further, the alumina nanotube of the invention can be applied for use ina secondary lithium battery.

The method of producing the alumina nanotube includes mixing asurfactant and an alumina precursor to create a mixture; adding water tothe mixture, followed by hydrothermal reaction and drying andcalcinating processes to remove residual surfactants.

As the surfactant for the above process, preferably, a cationicsurfactant of Chemical Formula 1, an anionic surfactant of ChemicalFormula 2, a non-ionic surfactant of Chemical Formula 3 or a neutralsurfactant of Chemical Formula 4, as depicted below are used.

wherein R₁ to R₃ represent substituted or unsubstituted alkyl group with1 to 4 carbon atoms, R₄ represents substituted or unsubstituted alkylgroup with 8 to 22 carbon atoms, and X represents a halogen atom,acetate, phosphate, nitrate, or methylsulfate.R₅—COOH  [Chemical Formula 2]wherein R₅ represents substituted or unsubstituted alkyl group with 1 to22 carbon atoms.CH₃(CH₂)₃₀(CH₂CH₂O)_(n)—OH  [Chemical Formula 3]wherein n represents an integer of 1 to 30.R₆—NH₂  [Chemical Formula 4]wherein R₆ represents substituted or unsubstituted alkyl group with 8 to22 carbon atoms.

Examples of cationic surfactants of Chemical Formula 1 includeCH₃(CH₂)_(n-1)N(CH₃)₃Br (n is 12, 14, 16 or 18),CH₃(CH₂)_(n-1)N(CH₃)₃Cl(n is 12, 14, 16 or 18). The size of a mesoporedepends on the length of the cationic surfactant's tail. Therefore, acationic surfactant with an appropriate tail length may be chosendepending on the desired size of the mesopore.

Examples of anionic surfactants of Chemical Formula 2 includeCH₃(CH₂)₁₀COOH, CH₃(CH₂)₁₂COOH and CH₃(CH₂)₁₄COOH and CH₃(CH₂)₁₆COOH.

Examples of nonionic surfactants of Chemical Formula 3 includeCH₃(CH₂)₁₅—(CH₂CH₂O)₂—OH, CH₃(CH₂)₁₅—(CH₂CH₂O)₁₀—OH andCH₃(CH₂)₁₅—(CH₂CH₂O)₂₀—OH.

Examples of neutral surfactants of Chemical Formula 4 includeCH₃(CH₂)₁₁NH₂, CH₃(CH₂)₁₃NH₂ and CH₃(CH₂)₁₅NH₂.

The surfactants of the foregoing may be used alone or in a combination.Preferably, the amount is 0.1 to 10 mole of the surfactant per 1 mole ofthe aluminum alkoxide precursor. If the amount of the surfactant is lessthan 0.1 mole ratio, the surfactant cannot effectively form micellestructures and when the amount is greater than 10 mole ratio, it is notcost effective to use such surplus amount of surfactants.

As an alumina precursor, any commonly used material in the field may beused. However, preferably, an aluminium alkoxide is used. Examplesinclude aluminium tri-sec-butoxide and aluminium isopropoxide.

Such alumina precursor, such as aluminum alkoxide, undergoes rapidhydrolysis, forming a hydrated hydroxide, so that additives are used torestrain hydrolysis. However, in the present invention, the hydrolysisrate can be controlled simply by adding water, without adding additives.

Preferably, the amount of water used in hydrolysis is determinedaccording to the stoichiometric ratio to the alumina precursor.Preferably, water is added slowly into a mixture of an alumina precursorand a surfactant in an organic solvent. Also preferably, thestoichiometric ratio of water to alumina precursor is 0.1 to 10 mole ofwater per 1 mole of alumina precursor and more preferably 1 to 3 mole ofwater per 1 mole of alumina precursor. At an amount less than 0.1 moleratio, it is difficult for an effective hydrolysis of aluminiumprecursor to take place, and when the amount is greater than 10 moleratio, the rate of hydrolysis increases due to large amount of water,making the formation of uniform mesopores difficult.

In the process of the invention for preparing a molecular sieve, themixture of a surfactant and an aluminium precursor in an organic solventis added with water and then subjected to hydrothermal reaction. Thepurpose of the hydrothermal reaction is to form an alumina mesoporeprecursor from the dehydration reaction of the mixture containing thesurfactant, aluminium precursor and the organic solvent. Preferably, thetemperature during the reaction is 0 to 200° C. and the reaction lasts10 to 100 hours.

After the hydrothermal reaction, drying and calcination processes arecarried out to produce a mesoporous alumina molecular sieve. Preferably,the drying process is done at a room temperature or at a sufficientlyhigh temperature to effectively remove un-reacted materials andsolvents. The temperature may vary according to the amount of addedwater and solvents. The purpose of the calcination process is to removeresidual surfactants. Preferably, the process is done at an inertatmosphere or at an air atmosphere for 1 to 10 hours at 200 to 800° C.

The invention further includes an alumina nanotube with lithium. Thelithium can be added simultaneously or after the alumina nanotubereaction. When adding lithium after the alumina nanotube reaction,ion-exchange method or impregnation method is used to incorporatelithium into the alumina nanotube.

Lithium can be effectively added during nanotube reaction by addinglithium precursor while the surfactant, alumina precursor and water arebeing mixed. Preferably, the amount of lithium precursor is 0.1 to 10mole per 1 mole of alumina precursor and more preferably, 1 to 3 moleper 1 mole of alumina precursor. Also preferably, the lithium precursoris lithium hydroxide, halide, nitrate, carbonate or sulfate. If theamount is less than 0.1 mole ratio, an effective chemical bondingbetween lithium precursor and alumina precursor is difficult to obtain,and at an amount of greater than 10 mole ratio, an effective chemicalreaction may not occur because of the small amount of aluminiumprecursor compared to the lithium precursor.

Besides adding the lithium precursor during the alumina nanotubereaction as described in the foregoing, lithium precursor may be addedafter the alumina nanotube has been produced.

In order to add lithium precursor to a pre-produced alumina nanotube, alithium precursor is added to impose ion exchange of the lithiumprecursor in the aqueous solution of the nanotube, followed by dryingand calcinating processes to create an alumina nanotube with a lithiumseed. Afterwards, another impregnation process with lithium precursor isimposed to produce alumina nanotube with lithium.

A radical as defined in the invention to be a substituted orunsubstituted alkyl group with 1 to 4 carbon atoms includes suchradicals in linear or branched forms, and one or more of the radicalsmay be substituted with a halogen atom, hydroxy group, carboxyl group,cyano group or amino group. Examples of such radicals include methyl,ethyl, n-propyl, isopropy, n-butyl, isobutyl, sec-butyl and t-butyl.

A radical as defined in the invention to be a substituted orunsubstituted alkyl group with 1 to 22 carbon atoms includes suchradicals in linear or branched forms, and one or more of the radicalsmay be substituted with a halogen atom, hydroxy group, carboxyl group,cyano group or amino group. Examples of such radicals include methyl,ethyl, n-propyl, isopropy, n-butyl, isobutyl, sec-butyl, t-butyl,pentyl, isoamyl, hexyl, octyl, isooctyl, nonyl, lauryl, myristyl, cetyland stearyl.

A radical as defined in the invention to be a substituted orunsubstituted alkyl group with 8 to 22 carbon atoms includes suchradicals in linear or branched forms, and one or more of the radicalsmay be substituted with a halogen atom, hydroxy group, carboxyl group,cyano group or amino group. Examples of such radicals include octyl,isooctyl, nonyl, lauryl, myristyl, cetyl and stearyl.

The invention will now be described more fully with reference toexamples. This invention may, however, be embodied in many differentforms and should not be construed as being limited to the embodimentsset forth herein; rather, these embodiments are provided so that thisdisclosure will be thorough and complete, and will fully convey theconcept of the invention to those skilled in the art.

EXAMPLES Example 1-1 to 1-5

The method of synthesizing a mesoporous alumina molecular sieve is asfollows.

In 70 ml of 1-butanol, CH₃(CH₂)_(n-1)N(CH₃)₃—Br (n=12, 14 or 16) as acationic surfactant and aluminum tri-sec-butoxide as a alumina precursoras listed in Table 1 were mixed under stirring until a uniform mixtureis obtained. To the mixture, distilled water was slowly added. The moleratio of the mixture was 0.5:1:2 for surfactant:aluminumtri-sec-butoxide:distilled water, respectively. After the mixture wasstirred until a uniform mixture was obtained, the obtained mixture in agel form was moved into a Teflon-lined autoclave container, andhydrothermal reaction was carried out for 24 hours at temperatureslisted in Table 1. Afterwards, the product was washed with ethanolseveral times, the product was dried at room temperature for 16 hoursand followed by another 5 hours of drying at 110° C. Then, a calcinationprocess was carried out at 500° C. and at atmospheric pressure for 4hours to remove any residual surfactant, thereby producing themesoporous alumina molecular sieve. The mesopore distribution is shownin Table 1. Also, the TEM photograph of the mesoporous alumina molecularsieve in Examples 1-5 is shown in FIG. 7. FIG. 7 shows that acomparatively uniform mesopore has a similar structure as a worm-holedistribution.

TABLE 1 BET Specific Surfactant Temp. Time Surface area BJH Pore sizeCH₃(CH₂)_(n−1)N(CH₃)₃—Br (□) (h) (m²/g) (nm) Example 1-1 n = 12 100 24429 4.5 Example 1-2 n = 14 100 24 241 6.5 Example 1-3 n = 16 RT 24 3107.2 Example 1-4 n = 16 100 24 337 6.7 Example 1-5 N = 16 150 24 401 4.8

As Table 1 illustrates, the surface areas of mesoporous aluminamolecular sieves range between 241 to 429 m²/g. The BET surface area andBJH pore size of the mesoporous molecular sieves, determined by nitrogenisotherm absorption test, were dependent upon reaction temperature andthe tail length of the surfactants. As reaction temperature was raisedfrom room temperature to 423K, the pore size decreased from 7.2 nm to4.8 nm, and the pore distribution became narrower. Also, the pore sizeincreased with an increase in the tail length of the surfactants.Therefore, it can be inferred that by manipulating the condition duringreaction process, the size of the pore can be controlled.

FIG. 8 illustrates the representative small angle and wide angle X-raydiffraction patterns of the mesoporous alumina molecular sieve producedaccording to Example 1-4 of the invention. XRD pattern of the smallangle, which is known to be closely related to the distribution of thepores of the mesoprous alumina, showed only a single peak, which is anindication of irregular mesopore structure. The wide angle X-raydiffraction analysis indicates the correspondence between the mesoporousalumina molecular sieves and the bulk gamma-alumina peaks. These resultsindicate that the mesoporous alumina molecular sieves of Example 1-4 arecomposed of oxidized aluminium or aluminium oxyhydroxide with lowcrystallinity.

The pore structure of the mesoporous alumina molecular sieve of Example1-4 showed high uniformity, however, clear repetitive arrangements ofthe pore structures were not shown. Such irregular pore connectivity isconsidered to be similar to a worm-hole or a sponge like structure,often found in the mesopores of silica alumina. Although a consistentarrangement over a wide range is not shown, as the small angle X-raydiffraction analysis illustrates, a single strong peak indicates thateach of the pore channels possesses consistent distribution.

High resolution NMR allows for a structural analysis of aluminum in amesoporous alumina molecular sieve. For the present invention, ²⁷Al MAS(Magic angle spinning), CPMAS (Cross Polarization Magic Angle Spinning),MQMAS (Multiple Quantum Magic Angle Spinning) NMR experiments wereperformed for the molecular sieves of Examples 1-1 to 1-5, in regards toeach of the tail lengths. The results showed two clear resolution ²⁷AlNMR peaks, which indicate the presence of nonequivalent magnetic Alcenters. The two peaks are known to represent aluminum sites withtetrahedral and octahedral structures, respectively. Around 33 ppm, aweak NMR peak was observed, and this was a 5-coordinated aluminum site.²⁷Al CPMAS (Cross Polarization Magic Angle Spinning) NMR showed threeclear peaks at 72, 33 and −1 ppm. This is due to the increase in thecenter of the 5-coordinated aluminum due to a cross polarization effect.In other words, due to magnetization transfer from proton to aluminum,the corresponding NMR peak of 5-coordinated aluminum increased. Therehad been reports that such 5-coordinated aluminum center can function asa Lewis acid. Therefore, it can be assumed that the 5-coordinatedaluminum center in the molecular sieve synthesized by using a cationicsurfactant contains an electron receiving group.

The mesoporous alumina molecular sieve synthesized according to theinvention has similar structure to a worm-hole structure while having ahigh surface area, thermal stability and different coordinated aluminumsites than conventional molecular sieves.

Examples 2-1 to 2-5

Production of Alumina Nanotube

As illustrated in Table 2, CH₃(CH₂)_(n-1)N(CH₃)₃—Br (N=12, 14 or 16), asa cationic surfactant, and aluminum tri-secondary-butoxide as an aluminaprecursor were mixed under stirring until an uniform solution wasobtained. Distilled water was slowly added to the solution. The moleratio of such solution was 0.5:1:2 for surfactant:aluminumtri-secondary-butoxide:distilled water, respectively. After the solutionwas further stirred until it became uniform, the resulting solution, ina gel form, was moved into a Teflon-lined autoclave container, and wassubjected to hydrothermal reaction for 24 hours at temperatures listedin Table 1. Afterwards, the product was washed with ethanol severaltimes, and then the product was dried at room temperature for 16 hoursand for another 5 hours at 110° C. Then, after 4 hours of calcinatingprocess at 500° C. and at atmospheric pressure to remove residualsurfactant, an alumina nanotube composed of oxidized aluminum wasobtained.

BET BJH Surfactant(Cationic) Temp. Specific Surface Area Pore size(CH₃(CH₂)_(n−1)N(CH₃)₃—Br) (□) Time (h) (m²/g) (nm) Example 1-1 n = 12100 72 256 3.0 Example 2-2 n = 14 100 72 328 3.8 Example 2-3 n = 16 RT72 293 3.4 Example 2-4 n = 16 100 72 389 3.6 Example 2-5 n = 16 150 72385 3.8

The results in Table 2 indicate that with an increase in the carbonchain in the tail of the surfactants and temperature, the pore size andthe surface area increase.

Examples 2-6 to 2-9

Production of Alumina Nanotube

Various surfactants (cationic, anionic, nonionic, neutral) with 16carbon chains in the tail length were used to produce alumina nanotubes.The mixing ratio was same as for the examples 2-1 to 2-5, in that0.5:1:2 for surfactant, aluminum tri-secondary-butoxide, respectively,were used.

FIG. 1 represents the TEM photograph and SADP pattern of the aluminananotube produced by Example 2-6

TABLE 3 Temp. BET Specific Surface Area BJH Pore Size Surfactant (□)Time (h) (m²/g) (nm) Example 2-6 CH₃(CH₂)₁₅N(CH₃)₃—Br 150 72 385 3.8Example 2-7 CH₃(CH₂)₁₄COOH 150 72 282 2.8 Example 2-8 CH₃(CH₂)₁₅NH₂ 15072 300 2.8 Example 2-9 CH₃(CH₂)₁₅—(PEO)₂—OH 150 72 445 3.0

The results in Table 3 show that when surfactants with same tail lengthof carbon chain were used, the alumina nanotube of the present inventionshowed higher surface area than other conventionally used commercialbulk alumina.

Examples 2-10 to 2-13

Production of Alumina Nanotube with Lithium

In order to produce an alumina nanotube with lithium, a cationicsurfactant (CH3(CH2)n-₁N(CH₃)₃Br, n=16) or nonionic surfactant(—CH₃(CH₂)_(n-1)—C₆H₅—(PEO)_(x)—OH, n=8, x=8) as a surfactant, aluminumtri-secondary-butoxide as aluminum precursor, and lithium hydroxide,lithium chloride or lithium carbonate as lithium precursor, and water asa solvent were mixed according to Table 4. The mole ratio was 0.5:1:1:2for surfactant:aluminum precursor:lithium precursor:water, respectively.After the mixture was stirred until a uniform solution was obtained, theobtained solution was poured into a Teflon-lined autoclave container,and was subjected to hydrothermal reaction for 72 hours at 423K.Afterwards, ethanol was used to wash the product several times, and theproduct was dried at 383K. Then, after 4 hours of calcinating process at773K and at atmospheric pressure to remove residual surfactant, analumina nanotube with lithium was obtained.

Table 4 illustrates the reaction conditions (reaction temperature, typeof surfactant, type of lithium precursor) for the production of aluminananotubes with lithium.

TABLE 4 BET Specific BJH Pore Lithium Temp. Time Surface Area SizePrecursor Surfactant (K) (h) (m²/g) (nm) Example 2-10 LiOHCH₃(CH₂)₁₅N(CH₃)₃—Br 423 72 128 4.0 Example 2-11 LiClCH₃(CH₂)₁₅N(CH₃)₃—Br 423 72 234 6.2 Example 2-12 Li₂CO₃CH₃(CH₂)₁₅N(CH₃)₃—Br 423 72 137 10.0 Example 2-13 LiOHCH₃(CH₂)₇—C₆H₅—(PEO)₈—OH 423 72 136 3.0

FIG. 2 a represents HR-TEM photographs of an alumina nanotube withlithium, produced according to Example 2-10 of the invention.

FIG. 2 b represents TEM photographs of an alumina nanotube with lithium,produced according to Example 2-10 of the invention.

FIGS. 2 a and 2 b indicate that the alumina nanotube is composed ofbundle of lower nanotubes and the structure was confirmed by molecularsimulation.

Example 2-14

Production of Alumina Nanotube with Lithium

In producing an alumina nanotube with lithium, a lithium precursor maybe added on to an already produced alumina nanotube by post-treatment.

First, a cationic surfactant (CH₃(CH₂)_(n-1)N(CH₃)₃Br, n=16) as asurfactant, aluminum tri-secondary-butoxide as aluminum precursor andwater as a solvent were mixed together. The mole ratio was 0.5:1:2 forsurfactant:aluminum precursor:water, respectively. After the mixture wasstirred until a uniform mixture was obtained, the resulting solution waspoured into a Teflon-lined autoclave container, and was subjected tohydrothermal reaction for 72 hours at 423K. Afterwards, the product waswashed with ethanol several times, and then dried at 383K. Then, after 4hours of calcinating process at 773K and at atmospheric pressure toremove any residual surfactant, an alumina nanotube was obtained.

To the alumina nanotube, lithium is added to create a derivative ofalumina nanotube with added lithium as described below.

As a lithium precursor, LiNO₃ was used. In the already produced aluminananotube, 0.5 wt % of LiNO₃ per 1 g of the alumina nanotube and 100 mlof water were added to allow ion exchange for 3 hours at a roomtemperature. The resulting product was filtered, washed with distilledwater, and dried for 12 hours at 373K. The dried material was calcinatedat 623K for 5 hours and at an air atmosphere for 2 hours. After thematerial reached 573K, it was treated with oxygen for 2 hours to obtainan alumina nanotube with added lithium seed.

In the resulting alumina nanotube with added lithium seed, 5 wt % ofLiNO₃ was added again by an impregnation process followed by acalcinations process at 623K and at an air atmosphere to produce analumina nanotube with lithium.

FIG. 3 depicts the TEM photograph of the alumina nanotube with lithium.

Example 2-15

Hydrogen Storage by Using Alumina Nanotube

In Example 2-10, hydrogen storage capacity was tested by using thealumina nanotube with lithium.

FIG. 4 illustrates schematical view of the equipment used to performhydrogen storage experiments. The equipment is fixed volume equipmenthaving a hydrogen gas storage container (4) (83.52 ml) and a samplecontainer (6) (15.02 ml), where samples are to be added.

For hydrogen storage test, 0.1 g of alumina nanotube with lithium asproduced by Example 2-10, is inserted in the sample container (6) ofFIG. 4. Then, vacuum pump (5) was connected to the container and allother valves were closed. By using the vacuum pump, all foreignsubstances in the sample were discharged. For the process, by usingtemperature controller (7), the temperature of the electrical furnacewas preheated to a range between 473K and 673K and then reduced to298K-673K for the hydrogen storage test. After the temperature was set,all valves were closed, and then vacuum pump (5) was turned on.

After the temperature of the entire system was set to the appropriatehydrogen storage experiment temperature (298K-673K) and stabilized, thepressure control regulator was set to a constant pressure (2.7 atm).Afterwards, hydrogen storage container was filled with hydrogen, andwhen the pressure was stabilized, the reading on transmeter (3) wasrecorded. After recording readings at various pressures, the value ofthe pressure transmeter (3) was calibrated. Afterwards, it was confirmedthat no gas escaped from the entire system.

For the hydrogen storage test, hydrogen with ultrahigh purity (99.999%)in predetermined pressure (2.7 atm) was injected into the hydrogencontainer (6). The readings on the pressure transmeter indicator wererecorded with time.

The amount of hydrogen absorbed in an alumina nanotube was assessed bythe decreased value in the pressure. FIG. 5 shows the amount of hydrogenadsorbed under a constant pressure (2.7 atm) but at differenttemperatures. From FIG. 5, it can be inferred that the hydrogenadsorption speed and hydrogen storage capacity clearly increase with theincrease in the temperature. At a temperature above 473K, the hydrogenstorage capacity was similar for all samples (approximately 8.8 wt %).

Also, FIG. 5 shows that when hydrogen adsorbed (approx. 8.8 wt %) at473K, was re-vacuumed at 673K to be detached and readsorption test wascarried out, a smooth desorption and readsorption processes of hydrogenwere possible.

Experimental Example

The adsorption and desorption processes of the hydrogen during hydrogenstorage Experiment of 2-15 was confirmed by ¹H NMR and shown in FIG. 6.

“a” represents the result of ¹H NMR at room temperature, before hydrogenstorage, but after vacuum treatment, which showed that there was nohydrogen adsorption. “b” represents the result of ¹H NMR after 45 hoursof hydrogen storage test at room temperature and at 2.7 atmosphericpressure, which showed hydrogen adsorption. Afterwards, the adsorbedhydrogen was re-vacuumed and deabsorbed and ¹H NMR confirmed a completedesorbed as shown in “c.” Then, “d” showed that the hydrogenreadsorption had taken place.

The above examples and experimental examples show that the hydrogenstorage capacity by the alumina nanotubes produced according to thepresent invention, even in a mild environment (temperature andpressure), the hydrogen storage efficiency (approximately 8.8 wt. %) washigher than other commonly used hydrogen storage materials and alsoshowed smooth adsorption and desorption reactions. Accordingly, thealumina nanotube produced according to the invention is considered asafe and economical hydrogen storage medium.

Theoretically, the hydrogen storage capacity of a hydrogen storage unitusing a metal hydride is considered to be high, depending on the type ofthe metal (e.g. 10.6 wt % for LiAlH₂). However, ordinarily, it is knownthat an actual metal hydride only shows approximately 5 wt. % ofhydrogen storage capacity. Recently, there had been a report of highhydrogen storage capacity by using a carbon nanotube (approx. 20 wt. %).However many researchers are refuting the reproducibility of such resultsince most of other reports show approximately 5 wt % of hydrogenstorage capacity at an extremely high pressure (approx. 100 atm).Therefore, a new hydrogen storage medium using the alumina nanotube ofthe present invention can be useful.

As discussed above, the alumina nanotube produced by the presentinvention has the following advantages: compared to other production ofcarbon materials having nano structures, alumina nanotube production issimple and produces large quantity; the absorption and de-absorption canbe easily controlled by manipulating temperature and pressure during theuse as a hydrogen storage material; the inner structure does not easilychange form even after repeated adsorption—desorption reactions, therebyproviding a structural stability; and by proven accuracy andreproducibility, it provides great use as clean hydrogen energy source.

The mesoporous alumina molecular sieve of the invention is produced byusing a cationic surfactant without using traditionally used additives.Also, because the size and distribution of the pores can be controlled,the molecular sieve can be produced simply and economically, producingmolecular sieve with high surface area and thermal stability.

Further, the alumina nanotube of the invention, can be mass-produced ina mild condition, compared to other commonly used methods of nanotubeproduction. The alumina nanotube can be used as a hydrogen storagematerial since it can effectively store and safely transportcomparatively large amount of hydrogen in a small volume. Further, itcan be used in a lithium secondary battery.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims.

1. A method of producing a mesoporous alumina molecular sieve,comprising: mixing a surfactant and an alumina precursor with an organicsolvent to produce a mixture; adding water to the mixture; hydrothermalsynthesizing the mixture with the added water; and drying andcalcinating the mixture to remove residual surfactants, wherein thesurfactant is a cationic surfactant represented by chemical formula 1below:

wherein R₁ to R₃ represent substituted or unsubstituted alkyl group with1 to 4 carbon atoms, R₄ represents substituted or unsubstituted alkylgroup with 8 to 22 carbon atoms, and x represents a halogen atom,acetate, phosphate, nitrate, or methylsulfate.
 2. The method as claimedin claim 1, wherein the alumina precursor to water in mole ratio is1:0.1 to
 10. 3. The method as claimed in claim 2, wherein the aluminaprecursor to water in mole ratio is 1:1 to
 3. 4. The method as claimedin claim 1, wherein the surfactant to water in mole ratio is 1:0.1 to10.
 5. The method as claimed in claim 1, wherein the alumina precursoris an aluminum alkoxide.
 6. The method as claimed in claim 5, whereinthe aluminum alkoxide is an aluminum-tri-butoxide or an aluminumisopropoxide.
 7. The method as claimed in claim 1, wherein the organicsolvent is an alcoholic-based solvent.
 8. The method as claimed in claim7, wherein the organic solvent is 1-butanol, 2-butanol, 1-propanol or2-propanol.
 9. The method as claimed in claim 1, wherein thehydrothermal reaction is carried out at 0 to 200° C. for 10 to 100hours.
 10. A method of producing alumina nanotube, comprising: mixing asurfactant and an alumina precursor to produce a mixture; adding waterto the mixture; hydrothermal synthesizing the mixture with the addedwater; and drying and calcinating the mixture to remove residualsurfactants.
 11. The method as claimed in claim 10, wherein the aluminaprecursor to water in mole ratio is 1:0.1 to
 10. 12. The method asclaimed in claim 11, wherein the alumina precursor to water in moleratio is 1:1 to
 3. 13. The method as claimed in claim 10, wherein thesurfactant to water in mole ratio is 1:0.1 to
 10. 14. The method asclaimed in claim 10, wherein the surfactant is a cationic surfactant ofchemical formula 1 below, an anionic surfactant of chemical formula 2below, a nonionic surfactant of chemical formula 3 below, or a neutralsurfactant of chemical formula 4 below:

wherein R₁, to R₃ represent substituted or unsubstituted alkyl groupwith 1 to 4 carbon atoms, R₄ represents substituted or unsubstitutedalkyl group with 8 to 22 carbon atoms, and x represents a halogen atom,acetate, phosphate, nitrate, or methylsulfate;R₅—COOH  [Chemical Formula 2] wherein R₅ represents substituted orunsubstituted alkyl group with 1 to 22 carbon atoms;CH₃(CH₂)₃₀(CH₂CH₂O)_(n)—OH  [Chemical Formula 3] wherein n represents aninteger of 1 to 30;R₆—NH₂  [Chemical Formula 4] wherein R₆ represents substituted orunsubstituted alkyl group with 8 to 22 carbon atoms.
 15. The method asclaimed in claim 10, wherein the alcoholic group of organic solvents is1-butanol, 2-butanol, 1-propanol or 2-propanol.
 16. The method asclaimed in claim 10, wherein the hydrothermal reaction is carried out at0 to 200° C. for 10 to 100 hours.
 17. A method of producing aluminananotube, comprising: mixing a surfactant and an alumina precursor withan organic solvent to produce a mixture; adding water to the mixture;hydrothermal synthesizing the mixture with the added water; and dryingand calcinating the mixture to remove residual surfactants, and furthercomprising adding a lithium precursor during producing the mixture orafter the calcinating process.
 18. The method as claimed in claim 17,wherein the lithium precursor and water is added after the calcinatingprocess and further drying and calcinating to produce an aluminananotube with lithium, and again adding the lithium precursor byimpregnation method followed by calcinating process.
 19. The method asclaimed in claim 17, wherein the lithium precursor is a lithiumhydroxide, halide, nitrate, carbonate or sulfate.
 20. The method asclaimed in claim 17, wherein the alumina precursor to the lithiumprecursor mole fraction is 1:0.1 to
 10. 21. The method as claimed inclaim 17, wherein the alumina precursor to water mole fraction is 1:0.1to
 10. 22. The method as claimed in claim 17, wherein the aluminaprecursor to water mole ratio is 1:1 to
 3. 23. The method as claimed inclaim 17, wherein the surfactant to water mole ratio is 1:0.1 to
 10. 24.The method as claimed in claim 17, wherein the surfactant is a cationicsurfactant of chemical formula 1 below, an anionic surfactant ofchemical formula 2 below, a nonionic surfactant of chemical formula 3below, or a neutral surfactant of chemical formula 4 below:

wherein R₁ to R₃ represent substituted or unsubstituted alkyl group with1 to 4 carbon atoms, R₄ represents substituted or unsubstituted alkylgroup with 8 to 22 carbon atoms, and x represents a halogen atom,acetate, phosphate, nitrate, or methylsulfate;R₅—COOH  [Chemical Formula 2] wherein R₅ represents substituted orunsubstituted alkyl group with 1 to 22 carbon atoms;CH₃(CH₂)₃₀(CH₂CH₂O)_(n)—OH  [Chemical Formula 3] wherein n represents aninteger of 1 to 30;R₆—NH₂  [Chemical Formula 4] wherein R₆ represents substituted orunsubstituted alkyl group with 8 to 22 carbon atoms.
 25. The method asclaimed in claim 17, wherein the aluminum precursor is a aluminumalkoxide.
 26. The method as claimed in claim 17, wherein thehydrothermal reaction is carried out at 0 to 200° C. for 10 to 100hours.
 27. An alumina nanotube produced by the method of claim
 10. 28. Ahydrogen storage material produced by inducing absorption of hydrogen tothe alumina nanotube of claim
 27. 29. A hydrogen storage material ofclaim 28, wherein the absorption of hydrogen is carried out whilemaintaining temperature of a container holding the nanotube at 298K to673K and maintaining the pressure of hydrogen gas at 1 to 10 atmosphericpressure.
 30. The hydrogen storage material of claim 29, wherein thecontainer holding the nanotube is vacuum treated at 373K to 773K priorto inducing hydrogen adsorption.